1. Field of the Invention
The invention concerns a mechanical counter for a metering apparatus for metering powder, liquid or gaseous substances, and metering apparatus comprising such a counter. The apparatus comprises inter alia two coaxially arranged housing portions which are rotated relative to each other upon actuation of the apparatus. The number of metering portions of the substance is counted and displayed by the counter.
An aim of the invention is to provide optimum adaptation of a counter of that kind to handling of the metering apparatus in an operationally reliable manner, and to simplify manufacture of the counter.
2. Related Art
The invention has been particularly, though not exclusively, developed for application to metered dose inhalers (MDI's) such as are disclosed in U.S. Pat. No. 5,497,944 (derived from WO91/14468), the entire contents of both of which are incorporated herein by reference. Pressure (generally at least 50 bar) is generated in a metered amount of fluid which is discharged through a nozzle assembly having one or more very small openings e.g. in the range 25 to 500 square micrometres. Preferred nozzle assemblies are disclosed in U.S. Pat. No. 5,472,143 (and parallel WO94/07607), the entire contents of both of which are incorporated herein by reference. An energy storage means, such as a spring, is preferably manually loaded e.g. by a rotary sawtooth wedge arrangement as disclosed in U.S. Pat. No. 4,260,082 and GB Patent Application 2291135, the entire contents of both of which are incorporated herein by reference. A latching mechanism is generally provided to hold the spring in the loaded position and is manually releasable to pressurise the metered amount of fluid e.g. using a piston and cylinder arrangement. A reservoir and valve arrangement can be provided for recharging the cylinder. Further details are described in PCT/EP96/04351 and parallel U.S. Ser. No. 08/726219, the entire contents of both of which are incorporated herein by reference.
Metering apparatuses are used for example in medical aerosol therapy for dealing with ailments of the respiratory tracts. In that situation a liquid or powder medicament is atomised to form an aerosol by means of an atomiser or entered into a stream of gas. The medicament is contained in a supply container which is inserted into the metering apparatus. The supply in a container may be sufficient for several days up to some months. It is therefore necessary to display the consumed amount of medicament or the amount of medicament which is still present in the container.
PCT Patent Publication WO-93/24167 provides a display device for a medical metering apparatus. That display device comprises a ring which is rotatable in coaxial relationship with respect to the apparatus and which, for each dose of a medicament under pressure which is taken from the metering apparatus, is automatically rotated through a predetermined angle by a wedge drive, a small portion of the ring being visible. The display device is pneumatically actuated when the medicament is inhaled.
U.S. Pat. No. 4,817,822 discloses a display device for a metering apparatus, the display device comprising a linear or a rotatable disk-like scale which is disposed beside the metering device and which is moved by means of a locked wheel and a locking pawl. Only a small portion of the scale is visible through a window.
PCT Patent Publication WO-86/05991 describes a display device for a metering apparatus, which device comprises a disk-like scale with teeth on the periphery of the disk, and is rotated by means of a helix member. Only a small portion of the scale is visible through a window.
PCT Patent Publication WO-92/09324 discloses a display device for a metering apparatus in which the axial movement of the supply container within the housing is transmitted by means of a locking pawl and a worm gear to a rotatable scale of which a small portion is visible through a window.
In accordance with PCT Patent Publication WO-86/02275 a display device for a medical spray apparatus comprises a digital mechanical counter which is advanced by the movement of the supply container within the housing as soon as a dose of the substance is taken from the supply container. That apparatus comprises a large number of individual parts.
A display device which is actuated pneumatically or mechanically upon displacement of the supply container, which is under pressure, in the housing of the metering apparatus, is unsuitable for a metering apparatus having two housing portions which are rotatable relative to each other and a supply container which is fixedly disposed in the metering apparatus.
Ways were therefore sought of providing a suitable mechanical counter for a metering apparatus having two housing portions which are rotatable relative to each other.